The effects of intraruminal infusions of sucrose and xylose on nitrogen and fibre digestion in the rumen and intestines of cattle receiving diets of grass silage and barley

Abstract

Two male cattle (live weight 240 kg) fitted with rumen and simple T-piece duodenal cannulas were given a basal diet of 12 kg of silage (227 g/kg DM, 25.7 g N/kg DM), 1 kg of rolled barley and 100 g of mineral mixture. In addition to the basal diet, 0, 450 or 900 g/d of either sucrose or xylose was continuously infused intraruminally. The amount of organic matter (OM) entering the duodenum (P < 0.001) and excreted in the faeces (P < 0.01) was linearly increased with the increased sugar infusion. The proportion of digestible OM apparently digested in the rumen averaged 0.694, and did not differ (P > 0.05) with the level or type of sugar. Rumen ammonia concentration and molar proportions of isovalerate were decreased (P < 0.001) with increased sugar level. The decrease in the ammonia concentration was slightly less (P < 0.05) with xylose than with sucrose. Molar proportions of acetate, propionate and butyrate were not affected by the sugar level but sucrose produced a lower (P < 0.05) proportion of acetate and higher (P < 0.01) proportion of butyrate than did xylose. There was a net loss of N (11.6g/d) between the mouth and duodenum when the basal diet was consumed alone but a net gain (21.6 g/d) with the high level of sugar infusion. Microbial N flow at the duodenum, measured on the basis of RNA purine bases, increased linearly (P 0.05) for sugar levels of 0, 450 and 900 g/d, respectively. The amount of microbial N produced was closely related to rumen ammonia concentration (r—0.86; P < 0.001) and outflow of water at the duodenum (r 0.83; P